Drug delivery devices, such as pen type drug delivery devices, have application where regular injection by persons without formal medical training occurs. This may be increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease. In practice, such a drug delivery device allows a user to individually select and dispense a number of user variable doses of a medicament. The present disclosure is, in general not limited to variable dose devices, but would also be applicable for so called fixed dose devices which only allow dispensing of a predefined dose without the possibility for the user to increase or decrease the set dose.
There are basically two types of drug delivery devices: resettable devices (i.e., reusable) and non-resettable (i.e., disposable) devices. For example, disposable pen delivery devices are supplied as self-contained devices. Such self-contained devices do not have removable pre-filled cartridges. Rather, the pre-filled cartridges may not be removed and replaced from these devices without destroying the device itself. Consequently, such disposable devices need not have a resettable dose setting mechanism. The present disclosure is applicable for both types of devices, i.e. for disposable devices as well as for reusable devices.
Drug delivery devices, particularly pen delivery devices (so named because they often resemble an enlarged fountain pen), generally comprise three primary elements: a cartridge section that includes a cartridge often contained within a housing or holder; a needle assembly connected to one end of the cartridge section; and a dosing section connected to the other end of the cartridge section. A cartridge (often referred to as an ampoule) typically includes a reservoir that is filled with a medication or drug (e.g., insulin). A movable, e.g. rubber type, bung or stopper is typically located at one end of the cartridge reservoir, and a top having a pierceable, e.g. rubber, seal or septum is typically located at the other, often necked-down, end. A crimped annular metal band is typically used to hold the rubber seal in place. While the cartridge housing may be typically made of plastic, cartridge reservoirs have historically been made of glass.
The needle assembly is typically a replaceable double-ended needle assembly. Before an injection, a replaceable double-ended needle assembly is attached to one end of the cartridge assembly, a dose is set, and then the set dose is administered. Such removable needle assemblies may be threaded onto, or pushed (i.e., snapped) onto the pierceable seal end of the cartridge assembly.
The dosing section or dose setting mechanism is typically the portion of the pen device that is used to set (select) a dose. During an injection, a spindle or piston rod contained within the dose setting mechanism, often also called drive mechanism, presses against the bung or stopper of the cartridge. This force causes the drug contained within the cartridge to be injected through an attached needle assembly. After an injection, as generally recommended by most drug delivery device and/or needle assembly manufacturers and suppliers, the needle assembly is removed and discarded.
A further differentiation of drug delivery device types refers to the drive mechanism: There are devices which are manually driven, e.g. by a user applying a force to an injection button, devices which are driven by a spring or the like and devices which combine these two concepts, i.e. spring assisted devices which still require a user to exert an injection force. The spring-type devices involve springs which are preloaded and springs which are loaded by the user during dose selecting. Some stored-energy devices use a combination of spring preload and additional energy provided by the user, for example during dose setting.
WO 2014/033197 A1 describes a manually driven drug delivery device with a housing, a dose setting button operable to set a dose by rotation relative to the housing, a number sleeve arranged within the housing such that at least a portion of the number sleeve is visible through a first aperture in the housing, a piston rod coupled to the housing and to a driver such that rotation of the driver relative to the housing causes the piston rod to translate relative to the housing, and a clutch mechanism releasably coupling the number sleeve and the driver. The piston rod is in threaded engagement with an inner housing and in threaded engagement with the driver such that the piston rod advances by a fixed displacement for each revolution of the drive sleeve.